1. Field of the Invention
The present invention relates to an apparatus for rotating and driving a magnetic disk, and, more particularly, to the construction of a hub support thereof.
2. Description of the Prior Art
In a driving device for a floppy disk having a size of 3.5 inches, for example, an apparatus for rotating and driving a magnetic disk as shown in FIGS. 4 and 5 is used. In FIGS. 4 and 5, a hub support 1 is secured to a spindle 4 rotatively driven by a driving source such as a motor. A base of a plate spring 3 is secured to the back of the hub support 1, and a driving pin 2 is mounted on the extreme end of the plate spring 3. This driving pin 2 extends through a window hole of the hub support 1 and projects through the surface of the hub support 1. The hub support 1 is formed from a molded product, for example, such as plastic magnet material (powdered ferrite mixed in a resin material). The hub support 1 is magnetized to form a magnetic attraction surface whereby when a ferromagnetic metal hub 5 secured to a center of a magnetic disk is placed on the hub support 1, the hub support 1 attracts the hub by virtue of a magnetic attractive force. An extreme end of the spindle 4 is fitted into a center hole 7 of the metal hub 5, and a driving pin 2 is inserted into an engaging hole 8 of the hub formed at an off-center position of the metal hub 5 so that when the hub support 1 is rotatively driven integral with the spindle 4, the driving pin 2 abuts the end edge of the engaging hole 8. Thereby, the driving pin 2 urges the hub 5 externally in a radial direction to rotate the hub 5 and the magnetic disk integral therewith while positioning the hub 5. On the hub support 1, a stopper 16 is provided which serves to prevent driving pin 2 from moving to the rear of the engaging hole opposite to the rotation direction of the hub support 1 so that driving pin 2 abuts the end edge of the engaging hole 8.
Since the hub 5 is attracted by the magnetic attractive force caused by the hub support 1 as described above, when the magnetic disk is removed from the rotating and driving apparatus, it is necessary to move the hub 5 away from the hub support 1 against the aforesaid magnetic attractive force. F represents the magnetic attractive force.
It is necessary to magnetize the hub support 1 so that the metal hub 5 for the magnetic disk will be magnetically attracted by the hub support 1 as described above. FIGS. 6 and 7 show an example of a magnetizing head and a magnetizing method using this magnetizing head. As shown in FIGS. 6 and 7, the magnetizing head 9 has a flat upper surface on which the hub support 1 is closely placed, and an escape hole 11 for the spindle 4 is vertically bored in the center thereof. A coil 13 is wound about a suitable core so as to form a magnetic pole in a vertical direction of the magnetizing head 9, and is composed of plural layers wound in a radial direction.
When the hub support 1 is magnetized by use of the magnetizing head 9, the hub support 1 is closely placed on the upper end of the magnetizing head 9 as shown in FIG. 7 and electrical energy is applied to the coil 13 to develop a magnetic field.
According to the conventional magnetizing head of the hub support, uniform magnetic fluxes are generated approximately over the whole surface so that the hub support tends to be magnetized approximately with uniform strength over the whole surface. However, the hub support is not uniformly structured but a window hole is formed in the periphery of the driving pin so that the driving pin extends through with a spatial allowance about it, and therefore, the magnetic flux density in the periphery of the window hole is low. Moreover, since the engaging hole of the disk with the driving pin of the hub is superposed with respect to the window hole of the hub support, the magnetic attractive force in the periphery of the driving pin becomes weaker than in that of other parts of the hub support with the result that an imbalance between the magnetic attractive forces occurs and the disk hub cannot be smoothly mounted on and removed from the hub support.
In view of the above, proposals have been made as disclosed in Japanese Utility Model Application Laid-Open No. 62-147162 and Japanese Patent Application Laid-Open No. 62-197953 in which a thickness of a magnet provided on a hub support is made to be smaller than that of other parts in the peripheral portion of a driving pin, or a thickness of a portion opposed to the driving pin of the magnet is made to be small, the magnetizing force is weakened, or a magnetizing pitch is narrowed to form a weak magnetic attractive portion in a portion opposed to the driving pin of the magnet, so that a uniform magnetic attractive force is attained over the whole surface of the hub support.
However, according to the aforementioned publications, the magnetic flux density is merely divided stepwise. Accordingly, the magnetic attractive force is not uniformly generated over the whole surface of the hub support. It is necessary to use a magnet having a special shape or a special magnetizing head having a magnetizing pattern which is nonuniform. Particularly in the case where a complicated magnetizing pattern is required, it has been sometimes impossible to attain such pattern by the mechanical process of a magnetizing head and the winding of a magnetizing coil.